等通道转角挤压镁合金的微观组织和力学性能

采用自制的90°模具,分析不同的ECAP挤压路径对AZ31镁合金变形后的微观组织和力学性能的影响;对挤压后的试样进行显微组织观察、硬度测试,研究等通道挤压工艺(ECAP)对AZ31镁合金的晶粒细化效果.结果表明:Bc路径晶粒细化效果较好,随着挤压道次增加,晶粒发生细化,7道次后晶粒尺寸由原来的70μm细化到4.8μm左右;硬度值随道次增加显著提高,3道次后达到最大值90.81MPa,之后随道次增加,硬度略有下降,趋于稳定.     

ECAP变形对H65黄铜β相形态和显微硬度的影响

采用能实现大变形的等通道转角挤压法(ECAP),对H65黄铜进行ECAP变形实验,分析了H65黄铜在经ECAP变形后β相形态和硬度的演变规律。结果表明:铸态时β相呈半连续网状和短棒状无方向性分布,经ECAP奇数次挤压,β相变成了长条状,分布方向确定,间距变得紧密;经ECAP偶数次挤压,β相变成了粗的短棒状,分布方向不定,间距变得稀疏;ECAP变形对H65黄铜试样硬度提升作用明显,铸态时硬度值为70.8 HV,在3道次ECAP挤压后硬度达到最大值239.3 HV;β相对合金整体硬度的贡献主要发生在第1道次挤压,随后道次的挤压β相自身硬度值变化不大。     

Al-Zn-Mg-Cu铝合金ECAP变形后的组织和性能

通过对退火态的Al-Zn-Mg-Cu系铝合金在523 K加热进行不同道次等径通道挤压(ECAP),采用120°模具在Bc路径下经10次ECAP变形后等效真应变达到6.2.试验结果表明,退火态合金试样ECAP挤压后晶粒明显细化,8道次之后晶粒细化趋于缓和,10道次后获得晶粒尺寸为0.8 μm左右的等轴状组织.性能测试结果表明:合金的显微硬度、抗拉强度及伸长率随着ECAP变形道次的增加而增大,ECAP提高了合金的综合力学性能,显著地改善了合金的塑性.     

等通道挤压镁合金的微观组织与硬度

对ZK60镁合金进行了C方式(相邻道次间旋转180°)等通道角挤压.采用光学显微镜、扫描电子显微镜和透射电子显微镜分析了试样ECAP变形前后的显微组织变化;采用显维维氏硬度计进行了硬度测试,并分析了ECAP变形对材料硬度的影响规律.结果表明:在ECAP挤压后的组织中有高密度的位错,它促成再结晶并晶粒细化到1～3μm;在经过6道次挤压后,合金的硬度达到76.3 HV.     

形变方式对模压形变H62黄铜组织的影响

采用平行模压和交叉模压两种模压形变方式细化H62黄铜,用光学显微镜、SEM和TEM观察了黄铜经不同模压形变方式后试样的显微组织.结果表明:H62黄铜经模压形变后的试样中出现了亚微米和纳米尺寸的形变孪晶.与平行模压试样相比,交叉模压后试样的晶粒尺寸更小,并在晶粒内有更密集和更均匀的亚微米和纳米尺寸的形变孪晶.通过对试样截面和表面显微硬度的分析:交叉模压形变后的试样比平行模压形变后的试样具有更好的组织均匀性和更高的硬度值.     

前处理T艺对Al-Zn-Mg-Cu合金ECAP的影响

研究了退火、固溶、双级时效以及回归(RRA)热处理4种前处理工艺对Al-Zn-Mg-Cu系铝合金多道次等径通道挤压(ECAP)变形过程的影响.试验结果表明,退火态试样在常温下只能进行2道次ECAP变形,而其余3种状态常温下经1次ECAP变形后便发生严重的开裂现象.退火处理后的试样采用523 K温度加热可进行多次ECAP变形,挤压后晶粒明显细化且逐渐向等轴状演化.8道次之后晶粒细化趋于缓和,10道次后等效真应变达到了6.2,晶粒为O.8 μm左右的等轴状.随着挤压道次的增加,试样显微硬度不断增大,且存在定量关系.     

铬含量对ECAP铜铬合金组织和显微硬度的影响

制备不同质量百分含量铬的铜铬合金试样,对合金试样进行等径角挤压(ECAP)处理。然后采用金相显微镜和硬度测试仪等进行合金微观组织和力学性能的研究。结果表明,铬合金元素在合金中以颗粒状均勺分布,ECAP加工的道次越多,晶粒细化程度越大。其中Cu-7.5wt%Cr和Cu-11.25wt%Cr合金经ECAP加工处理后晶粒细化效果最为明显。同时,经过ECAP后试样各表面的显微硬度值均有不同程度的增加。     

挤压道次对航空用工业纯铝ECAP组织和性能的影响

采用等通道转角挤压(ECAP)方法加工航空用工业纯铝以形成细晶结构,对其组织、力学性能以及腐蚀性能进行了测试,研究挤压道次对工业纯铝组织和性能的影响。结果表明:ECAP加工后工业纯铝试样基体晶粒变长并细化。随挤压道次(7道次前)增加,其拉伸强度与表面硬度上升,伸长率降低。经过ECAP加工后,试样腐蚀电位提高,点蚀电位正移,耐蚀性能得到改善。工业纯铝试样ECAP后表面属于点蚀类型,并随挤压道次增加,腐蚀区的数量逐渐降低。     

等通道挤压后镁合金的微观结构研究

对Mg-6Zn-IGd-0．6Zr合金在预热温度为350、400、450℃下进行了2、4、6道次的挤压。采用光学显锻镜和透射电子显微镜分析了试样ECAP变形前后的显微组织变化，采用显维硬度计对Mg-6Zn-1Gd-0．6Zr合金ECAP变形前后进行了硬度测试，采用X-射线分析法分析了ECAP变形过程中晶面的转动。结果表明：ECAP不仅能够将晶粒细化到纳米级，而且能够提高材料的硬度；Mg-6Zn-IGd-0．6Zr合金ECAP变形后晶粒内部出现高密度位错．促进动态再结晶，对细化晶粒起着重要的作用。     

前处理工艺对Al-Zn-Mg-Cu合金ECAP的影响

研究了退火、固溶、双级时效以及回归（RRA）热处理4种前处理工艺对Al-Zn-Mg-Cu系铝合金多道次等径通道挤压（ECAP）变形过程的影响。试验结果表明，退火态试样在常温下只能进行2道次ECAP变形，而其余3种状态常温下经1次ECAP变形后便发生严重的开裂现象。退火处理后的试样采用523K温度加热可进行多次ECAP变形,挤压后晶粒明显细化且逐渐向等轴状演化。8道次之后晶粒细化趋于缓和，10道次后等效真应变达到了6．2，晶粒为0．8μm左右的等轴状。随着挤压道次的增加，试样显微硬度不断增大，且存在定量关系。     

The influence of the equivalent strain on the microstructure and hardness of H62 brass subjected to multi-cycle constrained groove pressing

In this study, multi-cycle constrained groove pressing (CGP) were imposed on H62 brass sheet, numerically and experimentally. The relationship between the distribution of the von Mises equivalent strain, microstructure and hardness of H62 brass was investigated. The results show that the distribution of the equivalent strain is non-uniform within samples subjected to CGP, which in turn creates the corresponding non-uniformity in the microstructure and hardness of H62 brass. With the increase of the equivalent strain the grains of H62 brass become finer and the hardness is improved. The value and distribution of the equivalent strain in H62 brass affects the plastic deformation mode at different locations within the sample subjected to CGP.     

ECAP和轧制工艺对H65黄铜β相形态和抗拉强度的影响

开展H65黄铜等通道转角挤压和轧制试验,研究ECAP变形和轧制变形前后,试样β相形态和抗拉强度的演变。结果表明:铸态时,β相分布无方向性,呈半连续网状和短棒状;经奇数道次变形后,β相平行间距变得紧密,并与水平约成30°分布,成长条状;经偶数道次变形后,β相平行间距稀疏,取向不定,呈粗的短棒状;经任何道次的ECAP变形再经轧制后,β相平行间距减小,几乎全部变成水平分布,且变得更加细长。H65黄铜在ECAP变形过程中,随着挤压道次的增加,抗拉强度值整体表现为上升趋势;同一试样在ECAP变形后再经轧制其抗拉强度值变大。β相取向与拉伸轴线夹角越小,β相平行间距越窄,H65黄铜的抗拉强度值越大。     

Effects of La<Subscript>2</Subscript>O<Subscript>3</Subscript> on Mechanical Properties and Corrosion Resistance of H62 Brass

In this article, the effects of lanthanum oxide (La₂O₃) on the microstructure and mechanical properties of H62 brass were investigated by using the universal testing machine, Brinell hardness tester, optical microscope, and scanning electron microscope (SEM). Immersion corrosion and electrochemical measurements were carried out to identify the influence of La₂O₃ on the corrosion behavior of the H62 brass. The phase constitution, microstructure, and phase composition of the H62 brass were analyzed by x-ray diffraction, SEM, and energy-dispersive spectrometer, respectively. The results show that the microstructure of α phase changes from dendrite grains to equiaxed grains, and the content and distribution of β phase are improved significantly. When the La₂O₃ content reaches 0.8 wt.%, the H62 brass obtains favorable comprehensive mechanical properties and the strength and hardness decrease but elongation increases, which is conducive to plastic processing. In addition, under the optimum amount of 0.8 wt.% La₂O₃ content, the corrosion rate of immersion corrosion attains the minimum values: As 12.6 g m^?2 h^?1, it decreases by 24%; as the corrosion potential changes from ?1.1327 V to ?0.328 V, it increases by 70.9%; and as the corrosion current density decreases from ?2.833 mA mm^?2 to ?3.28 mA mm^?2 corrosion, it decreases by 15.78%, when compared with H62 brass.     

等径弯曲通道变形制备超细晶铜的热稳定性

室温下采用等径弯曲通道变形(Equal Channel Angular Pressing,ECAP)C方式进行了纯铜(99.95%)12道次挤压变形。通过等温和等时退火,研究ECAP变形后铜的退火行为,并研究了等径弯曲通道变形和退火后纯铜的显微硬度和显微结构变化。分析了ECAP应变量、退火时间和退火温度对超细晶铜的再结晶行为、抗软化性能的影响。结果表明:ECAP变形后的超细晶铜在退火过程中,表现出不连续再结晶现象;ECAP降低了铜的热稳定性,变形道次越高再结晶温度越低。退火后稳态晶粒尺寸随变形道次的增加而细化,硬度值随变形道次的增加而增大,回归分析表明,晶粒尺寸与硬度之间的关系符合Hall-Petch公式。     

Effect of soft Bi particles on grain refinement during severe plastic deformation

Two aluminum alloys, Al–8Zn and Al–6Bi–8Zn were subjected to equal channel angular pressing (ECAP) up to 5 passes at room temperature. The microstructural evolution and the grain refinement behavior of these alloys were systematically studied by electron backscatter diffraction (EBSD). After 5 passes of ECAP, ultrafine grained microstructures formed in both alloys. However, the grain structure in the Al–6Bi–8Zn alloy is much finer than that of Al–8Zn alloy, showing that the soft Bi particles have a strong influence on enhancing the grain refinement during ECAP. The strengths of the ECAP-processed materials were measured by hardness test and it showed that after 5 passes of ECAP, the hardness of the Al–6Bi–8Zn alloy was higher than that of the Al–8Zn alloy. The effects of soft Bi particles on the deformation behavior during ECAP and the final strength of the Al–6Bi–8Zn alloy were discussed.     

等通道转角挤压Al-Mg2Si合金的组织与性能研究

研究Al-Mg2Si合金经250℃等通道转角挤压后的微观组织与力学性能。维氏硬度及拉伸力学性能测试结果表明:经4道次ECAP挤压后,Al-Mg2Si合金的硬度、抗拉强度和延伸率均显著提高;8道次挤压后合金的塑性进一步提高,但其硬度和抗拉强度却有所下降。扫描电子显微镜和透射电子显微镜分析表明:经ECAP挤压后,原汉字状或骨骼状Mg2Si相显著碎化,且挤压道次越多,Mg2Si相的破碎效果越明显,合金组织也不断细化。对合金经较多道次挤压后硬度及抗拉强度反而有所下降的原因进行了分析。     

连续等径角挤压制备超细晶铜

介绍一种制备超细晶材料的新技术———连续等径角挤压,它将连续挤压技术应用于制备超细晶材料的等径角挤压工艺,解决了传统等径角挤压不能制备大尺寸超细晶材料的问题,该技术对超细晶材料的推广应用具有重要意义。通过DEFORM3D对铜的连续等径角挤压过程的数值模拟,得到变形过程中金属的流动、应变场和温度场情况,并对不同变形速度和摩擦条件下的变形过程进行比较,得到优化的工艺参数,并以此参数进行实验。实验结果表明,连续等径角挤压后铜的硬度明显上升,连续等径角挤压3道次后,硬度趋于饱和;连续等径角挤压12道次后,铜的平均晶粒尺寸为400 nm。     

黄铜晶间腐蚀机理的实验及模拟研究

目的为了探究黄铜在含氨介质中的晶间腐蚀加速试验方法,明确黄铜中Zn含量对晶间腐蚀敏感性的影响规律和机理。方法采用电化学方法加速实现了黄铜表面的晶间腐蚀过程,利用XRD和金相显微镜分析腐蚀产物及表面形貌,对比分析H70和H80黄铜的晶间腐蚀规律。使用Materials Studio中的DMol3模块模拟NH4+和NH3在H70和H80黄铜晶界表面的吸附和反应过程,对比腐蚀粒子在黄铜表面的吸附规律和反应能垒,揭示黄铜晶间腐蚀敏感性的机理。结果试验结果表明,在NH4Cl溶液中,以100倍自腐蚀电流密度恒电流处理的黄铜,在4 h内能够发生明显的晶间腐蚀。黄铜晶间腐蚀的产物主要为铜氨络合物和锌氨络合物,H70黄铜的晶间腐蚀敏感性大于H80黄铜。模拟研究表明,NH4Cl溶液中的NH4+会优先在黄铜表面的晶界处发生物理吸附,随后NH4+跨越1.15 e V(H70)和1.17 e V(H80)反应能垒分解为NH3和H+,其中NH3优先吸附于晶界中偏析的Zn原子顶位形成络合物,其次与晶界的Cu形成络合物,H70晶界中的Zn含量更高,因此H70的晶间腐蚀敏感性更强。结论通过电化学恒电流处理法将黄铜的晶间腐蚀发生时间从7 d减少到4 h,并通过量子化学计算和腐蚀产物分析确定了黄铜在NH4Cl溶液中发生晶间腐蚀的机理。     

Plastic deformation mechanism of ultra-fine-grained AA6063 processed by equal-channel angular pressing

Equal-channel angular pressing (ECAP) is an established method to produce ultra-fine-grained (UFG) materials with extraordinary mechanical properties. However, different methods to characterize the complex microstructure give contradictory results. Therefore an ECAP-processed UFG aluminum alloy AA6063 was characterized by various electron-microscopy-based methods such as backscattered electron contrast, electron backscatter diffraction, transmission electron microscopy and low-voltage scanning transmission electron microscopy. Only a skilful combination of all methods reveals the complete information about the microstructure which is needed to understand the results of the mechanical testing by nanoindentation, tensile tests and strain-rate jump test. The main difference is the amount of low-angle grain boundaries and high-angle grain boundaries which determine hardness, tensile and yield strength and strain-rate sensitivity of ECAP materials produced by different numbers of passes and routes. This is explained by the interaction of dislocations with the different grain boundaries.     

基于材料改性的等径角挤压的塑性后处理工艺

简要介绍了等径角挤压成形工艺的特点及目前仍存在的诸多问题,综述了等径角挤压的塑性后处理工艺及其研究进展。传统等径角挤压后再进行其他塑性工艺的后处理,可以有效克服等径角挤压工艺的不足;进一步细化晶粒、增强材料的强度和硬度、改善材料综合性能,是提高等径角挤压制备效率的有效途径。